The art of the present invention relates to eye surgical devices in general and more particularly to an improved and modified form of a microvitreoretinal (MVR) blade having elements and features especially suited for radial optic neurotomy (RON) as a treatment for central retinal vein occlusion (CRVO).
Central retinal vein occlusion (CRVO) is a relatively common condition, reported to occur in approximately 60,000 new patients each year within the United States. Its etiology is poorly understood, with a wide array of medical and systemic disorders debated as to their potential causative effect. CRVO is most commonly reported in patients aged 50 to 80 years, with a statistical tendency towards those patients suffering from hypertension and/or glaucoma. The natural history of this condition can result in loss of vision due to extensive intraretinal hemorrhage, macular edema, iris neovascularization, neovascular glaucoma, and ischemic retinal infarct. Spontaneous resolution is uncommon; rather, it is most widely reported to have catastrophic consequences to affected patients.
There is no effective curative therapy for CRVO. Panretinal photocoagulation can be effective in controlling neovascularization, while grid photocoagulation has been reported to be successful in resolving edema. However, neither therapy restores vision nor reverses the basic occlusive condition. Attempts to create a physiological shunt by way of a of high powered photocoagulating chorioretinal anastomosis has reported some success, but is similarly associated with a high rate of complications. Many theorize that the CRVO is associated with thrombus within the central retinal vein. As such, many developing therapies have concentrated on resolving the thrombus by means of cannulation of the central retinal vein and administration of “clot busting” agents (t-PA). While technically feasible, the clinical results and reproducibility of this procedure remain non-validated.
An emerging hypothesis suggests that CRVO is a vascular complication secondary to a compartment syndrome. This condition is created as the optic nerve enters the eye, experiencing a reduction in outer diameter from 3.0 mm to 1.5 mm at the optic nerve head. It is theorized that congenital anatomical variances, connective tissue, persistent myelin sheaths, ocular motion, and other factors may increase pressure within the scleral outlet-compartment, thereby resulting in CRVO.
A new surgical procedure, radial optic neurotomy, (RON) addresses this causative factor and, in so doing, potentially provides a curative effect. By inserting a knife radial to the optic nerve head and advancing a specified distance, the compartment syndrome may be relieved by relaxing the cribiform plate, scleral ring, and adjacent sclera. Unfortunately, the greatest potential complication of such a maneuver is hemorrhage. To address this complication, the present art device incorporates design elements and features which minimize this threat.
The present art device is best described as a radial optic neurotomy (RON) knife. The device comprises in its most basic form, a modified conventional microvitreoretinal (MVR) blade with a single sharp nasal portion edge rather than the two opposing sharp edges, both nasally and medially as found in conventional MVR blades. Prior art conventional microvitreoretinal (MVR) knives or blades introduce a significant risk during the RON procedure as the sharp nasal and medial edges may cause an inadvertent disruption or cutting of the central retinal vessels. The single sharp edge of the present art device allows for a radial incision of the optic nerve head, with the incision proceeding nasally. In the present art device, the medial edge, i.e. the edge opposite the single sharp edge, of the blade is specially dulled, thereby allowing atraumatic passage of the knife alongside the central retinal artery and central retinal vein. The present art device further provides a depth gauge or measuring technique via the inclusion of a mark at a desired penetration depth distance from the device tip. Prior art conventional microvitreoretinal (MVR) knives or blades are unmarked, thereby leaving the surgeon without indication as to the actual depth of penetration. This mark provides the surgeon with a specific reference as to the depth of the radial incision, thereby minimizing the potential for globe perforation.
Accordingly, it is an object of the present invention to provide a device for radial optic neurotomy having a sharp edge and a medial dulled edge which is capable of atraumatic passage alongside the central retinal artery and central retinal vein.
Another object of the present invention is to provide a device for radial optic neurotomy having a depth gauge or measuring technique to optimize a desired penetration depth.